[feature] Allow setting schedule per Group

**Version and OS**
0.48.01 docker

**Is your feature request related to a problem? Please describe.**
I really like the new Scheduler feature but it's going to be tedious to set it up for the pages I have.

**Describe the solution you'd like**
These pages are already grouped and so I would really love to see the option of setting the schedule per group

**Additional context**
In general, I think the more settings will be available on the group level, the better and easier it will be for us to maintain many pages - https://github.com/dgtlmoon/changedetection.io/issues/2049

No files or tests are named. Start by locating the existing Scheduler feature and the group-level settings, then read the related issue 2049 for context; done means a schedule can be set for a group and applies to its pages without configuring each page individually.

Written by the indexing model from the issue text.